[sldev] Uses of LLString and std::string ?

[Steve Linden]

Correct, LLString exists specifically to protect against passing a NULL 
char* to a function that takes a const std::string&. C++ will quietly 
attempt to convert the NULL char* into a std::string causing a crash.

e.g.

foo (const std::string& s)
{
}
bar (const char* c)
{
    foo(c); // crashes if c is NULL
}
main()
{
    const char* s = fetchSomeString(); // returns NULL if it fails
    foo(s); // crash!
}

Note: we -still- have thousands of char arrays and char*'s in the code, 
and this pattern exists all over the place, especially in the UI code. 
We are actively working on eliminating this pattern. Once we do, we can 
safely replace LLString with std::string.

Because of the expense of converting a std::string to a LLString, we try 
to use LLString anywhere we will pass it as a std::string. However, in 
the grand scheme of things this is unlikely to be a significant 
performance bottleneck so we are not as paranoid about it as we might be.

-Steve

Dave Parks wrote:
> I believe the point of LLString is to protect against NULL pointer 
> assignments.  It's legacy from a time when we used char* strings and 
> began mixing in std::string.  Assigning a standard string to NULL 
> dereferences NULL, causing a crash.  LLString protects against this by 
> checking for NULL on assignment for char* strings.
>
> Alissa Sabre wrote:
>> I have a question.
>>
>> SL viewer uses two data types LLString and std::string, that are
>> almost identical.  They are sometimes intermixed.  LLString to
>> std::string conversion is by a simple upcasting, but the opposit is by
>> a deep copy through a constructor that requires some overhead.
>>
>> What is the purpose of LLString?  In case it has some, then the next
>> question is why LL uses both LLString and std::string?  (Cf. LL never
>> uses C++ bool type.)
>>
>> Assuming there is a good reason to use both LLString and std::string
>> in SL viewer, what is the criteria (or guidelines) to choose from
>> LLString and std::string?
>>
>>     Alissa Sabre
>> --------------------------------------
>> Easy + Joy + Powerful = Yahoo! Bookmarks x Toolbar
>> http://pr.mail.yahoo.co.jp/toolbar/
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